The present invention relates generally to a transaxle for transmitting power continually to the front wheels of a motor vehicle. More particularly, the invention pertains to a transaxle that contains an inter-wheel differential and an actively controlled, on-demand clutch.
In the powertrain of an all-wheel drive motor vehicle, whose engine and transaxle are transversely mounted in an engine compartment at the front of the vehicle, it is conventional for the transaxle case to contain a bevel-pinion differential mechanism, which is driven from the transmission's output and is driveably connected to the front halfshafts. The space that is enclosed by the transaxle case is relatively small. But an open, bevel gear differential mechanism requires a relatively large volume in the transaxle case. To overcome this difficulty, an additional component, a rear drive unit (RDU) such as a transfer case, is located in the driveline between the transaxle and a rear differential. The RDU contains an on-demand transfer clutch assembly, which transmits a portion of the torque to the rear axles depending on the degree to which the clutch is slipping or fully engaged.
The on-demand clutch couples a rear drive shaft to the transaxle output. These coupler assemblies require a pump, hydraulic control bodies, electronic controllers and lubrication systems, which are located in the transaxle, to control and actuate the on-demand clutch in the RDU. If, however, the components that produce the function of the RDU or transfer case could be integrating with the transaxle case, the powertrain would have fewer components, lower cost and improved operating reliability.
Current front-wheel drive vehicles that have no all-wheel drive capability use an open differential mechanism in the transaxle to transmit power differentially to the front wheels. When one front wheel is on a low friction surface, that wheel will tend to spin freely reducing vehicle traction on the road surface. Integrating a clutch between the differential's outputs to the right-hand side and left-hand side halfshafts provides a component that can be controlled to reduce wheel slip, thereby improving vehicle traction.
The clutch could be configured so that it controls the magnitude of torque transmitted between the differential's input and one of the side outputs or both outputs.
The differential mechanism could be a bevel gear differential or a compound planetary gearset. The on-demand clutch could be controlled hydraulically from the same controls used to operate the automatic transaxle.